A high degree of interest has been shown over the past years in the field of theft detection using electronic article surveillance systems wherein electronically sensitive devices, know as markers, are introduced into a electromagnetic field known as an interrogation zone, to emit a signal in response to such magnetic field. Electronic article surveillance (EAS) systems and markers for use therein were disclosed by P.A. Picard in French Patent Number 763,681 (1934). Generally, certain ferromagnetic alloys exhibit high magnetic permeability and low coercivety thereby making their use as EAS marker attractive. Materials for such markers have been made as disclosed in U.S. Pat. Nos. 4,581,524 and 4,568,921 and U.S. patent application Ser. No. 290,547. Although these markers generally work well, without the ability to deactivate such markers, i.e. rendering them unresponsive in an interrogation zone, the use of EAS systems becomes limited. For example, when an article with a marker attached thereto is purchased in a first store and the purchaser subsequently enters a second store with the article bearing the marker, the marker could generate an alarm in the EAS system of the second store unless measures are taken to avert the same. As is generally known, there are walk around systems as used in institutions such as libraries where the books are checked out. Thereafter, the individual walks through the gates of the EAS system without the book and is then given the book as it is it is passed around the gates. Although this system works well in controlled areas, such as libraries, it is not adequate in the commercial use of EAS systems.
In U.S. Pat. No. 3,747,086, a deactivatable marker is described that has a soft magnetic strip which is detectable in an interrogation zone of an EAS system. In addition to such soft magnetic strip, two hard magnetic strips elements are placed adjacent to the soft magnetic strip and these have distinctive magnetic properties which are not the same as the detectable soft magnetic strip. After a marker has been used for the purposes of theft detection, it is then deactivated by placing the marker in a magnetic field of high strength to magnetize the two hard magnet strips thereby rendering the marker undetectable. Although this marker functions adequately, it requires a relatively high magnetic field in order to deactivate the marker. Such high magnetic field is not only energy inefficient, and expensive, but also could present health hazards to those about the high magnetic field for extended periods. Furthermore, a relatively high amount of magnetic material is used in such prior art deactivatable markers.
It clearly would be advantageous to provide an EAS marker that can be readily deactivated in a relatively low magnetic field and uses a low quantity of magnetic material.